A number of potential advantages have led the automotive industry to look with increasing interest toward utilizing common rail high pressure direct injection for gasoline engines. Certain difficulties seem to stand in the way of fully achieving the advantages.
The pressurization of fuel to high levels (e.g., above 100 bar) requires considerable pumping power, which generates considerable heat. Moreover, the industry is looking to even higher rail pressures, above 200 bar. This heat could be dissipated to a large extent, if all the fuel that is pressurized can be quickly injected into the engine cylinders. This is not possible, however, because the fuel pump flow rate is typically sized for engine cranking, which may be at 20-30 bar pressure at a relatively high quantity flow rate, whereas typical steady state cruising conditions would require much lower quantity flow rates at 100 bar. Therefore, in a conventional pumping scheme, the volume of fuel raised to injection pressure during the course of an hour of typical vehicle use, is much greater than the volume of fuel actually injected during that same hour of use. Although pre-metering and various spill control techniques can be used to some advantage in this regard, none of these techniques satisfactorily regulates the power output of the high pressure pump itself.
Another difficulty is encountered with high pressure pumps that are driven directly by the engine (e.g., crank shaft, cam shaft, accessory belt). During transients when fuel demand is low (e.g., downhill or during gear shifting), the engine continues to turn and the pump continues to deliver high pressure fuel to a common rail that may already be at maximum pressure.
In the invention, a high pressure rotary pump is intimately coupled to an electric motor as a packaged unit situated at the vehicle fuel tank, with the speed of the motor and thus the pumping rate of the high pressure pump, being responsive to the rail pressure. Thus, the motor can quickly increase the drive shaft speed and thus provide high pumping volume during cranking, while reducing speed to a low level with, associated low pumping volume when the vehicle is cruising. Similarly, the motor can intermittently increase speed as needed to accommodate load demand during acceleration, or in essence stop the pump drive when the vehicle is coasting. The aspects sought to be protected, concern the manner in which the motor and pump are integrated and function together as a package.
Briefly stated, the invention in a preferred form is a pump for supplying high pressure fuel from a fuel tank to an engine via a common rail. The pump includes a motor assembly mounted on top of the fuel tank, a pump assembly positioned within the fuel tank, and a support column connecting the motor assembly to the pump assembly. The pump assembly comprises a high pressure pump sub-assembly including a pump body having a drive bore and multiple plunger bores formed therein, where a radially inner end of each plunger bore opens into the drive bore. The external profile of a drive member which is rotatable within the drive bore engages the radially inner end of pumping plungers disposed in each of the plunger bores for a portion of each revolution to reciprocally move the plungers between radially inner and outer limit positions. Reciprocation of each pumping plunger towards the inner limit position induces a low pressure in the outer end of the plunger bore, thereby drawing fuel into the outer end of the plunger bore via the drive bore without the aid of a low pressure pump. Reciprocation of each pumping plunger towards the outer limit position induces a high pressure in the outer end of the plunger bore, thereby discharging fuel from the outer end of the plunger bore into the common rail via the high pressure line.
The pump assembly also comprises a fine filter sub-assembly mounted to the top end portion of the pump body. The fine filter sub-assembly includes a cannister having an upper sleeve portion, a middle housing portion, a radially extending shoulder connecting the sleeve portion to the housing portion, and a lower mounting portion separated from the housing portion by a circumferential, radially inward extending protrusion. The top end portion of the pump body is received within the cannister mounting portion such that the protrusion rests on the pump body. An O-ring disposed in a circumferential groove in the top end portion of the pump body provides a fluid-tight seal between cannister and the pump body. Fuel vapor is vented from the fine filter sub-assembly via a vent orifice in the shoulder, with a check valve positioned in the vent orifice preventing backflow into the cannister. The outer surface of fine filter element disposed within the cannister housing portion, together with the inner surface of the cannister housing portion, forms an annular column and the inner surface of the fine filter element forms a cavity in fluid communication with the drive bore.
The pump assembly also comprises a coarse filter sub-assembly a coarse filter sub-assembly mounted to the bottom end portion of the pump body. The coarse filter sub-assembly includes a housing having an inlet in fluid communication with the fuel tank and an outlet in fluid communication with the annular column of the fine filter assembly. A coarse filter screen, is disposed intermediate the inlet and outlet of the housing. The housing further has a plurality of downwardly extending, circumferentially spaced spacers defining a plurality of slots which form the inlet. Each of the spacers has a bottom end which engages the inside surface of the bottom of the fuel tank to position the coarse filter screen at a distance above the fuel tank inner surface.
According, it is an object of the present invention to provide a high pressure gasoline common rail direct injection fuel supply system, in which the high pressure discharge of the means for raising and maintaining the rail pressure above 100 bar, is responsive to engine demand. The energy imparted to the discharged fuel (e.g., pressure increase) is over time, significantly reduced relative to conventional systems.